Equine neurology: central Flashcards
Identify the signs of central and peripheral disorders of the nervous system in horses
- Central: ataxia, seizures/collapse, blindness, autonomic dysfunction (bladder, GIT, other)
- Peripheral: weakness, autnomic dysfunction (bladder, dysphagia, GIT)
List the common disorders of the nervous system in horses
- Botulism
- Equine herpesvirus
- Equine degenerative myeloencephalopathy (EDM)
- Peripheral neuropathies
- Equine Grass Sickness
- Idiopathic hypersomnia
- Hepatic encephalopathy
- Perinatal asphyxia syndrome
- Idiopathic headshaking
- Vestibular disease
List the uncommon, but important disorders of the nervous system in horses that should always be placed on the differentials list
- Viral encephalitidies
- Polyneuritis equi
- Horners syndrome
- Epilepsy incl. benign epilepsy of Arab foals
- Narcolepsy
- Rye grass staggers
- Bacterial meningitis
- Equine protozoal myeloencephalitis
- Toxicities
List the uncommon disorders of the equine nervous system that can be managed independently
- Cervical vertebral malformation
- Tetanus
What is the most important central nervous system disease of horses in the UK?
Ataxia due to cervical vertebral disease
What is the most important peripheral nervous system disease of horses in the UK?
Equine grass sickness
List the differentials for central neurological disease of horses that fall into the “degenerative” category
- Cervical Vertebral malformation (type 1 juvenile onset, type 2 adult onset osteoarthritis)
- Equine degenerative myeloencephalopathy
List the differentials for central neurological disease of horses that fall into the “Anomalous” category
- Benign epilepsy of Arabian foals (not just Arabs)
- Narcolepsy
- Hydrocephalus (foals, severe ataxia, intention tremor)
- Occipitoatlantal malformations
- Cerebellar abiotrophy (progressive cerebellar degeneration)
List the differentials for central neurological disease of horses that fall into the “metabolic” category
- Hepatic encephalopathy
- Perinatal asphyxia syndrome
- Hypoglycaemia, Electrolyte abnormalities (both uncommon)
List the differentials for central neurological disease of horses that fall into the “nutritional” category
Equine Degenerative Myeloencephalopathy
List the differentials for central neurological disease of horses that fall into the “neoplasia” category
- Pituitary Pars Intermedia Dysfunction
- Others rare: hamartoma, cholesterinic granuloma, epidural lymphosarcoma
List the differentials for central neurological disease of horses that fall into the “inflammatory infectious” category
- Bacterial: bacterial meningitis (foals), abscessation
- Spirochete: Borrelia burgdorferi
- Viral: EHV, togaviridae, Flavivirus, Hendra virus, Borna, Rabies
- Other: Equine protozoal myeloencephalitis
Which of the viral infectious that cause neurological signs in horses are notifiable?
- Togavirus (Eastern, Western, Venezuelan equine encephalitis)
- Flavivirus (West Nile virus, Japanese encephalitis)
- Hendra virus
- Borna virus
- Rabies
List the differentials for central neurological disease of horses that fall into the “idiopathic” category
- Idiopathic hypersomnia
- Idiopathic epilepsy
- Narcolepsy
- Idiopathic headshaking
List the differentials for central neurological disease of horses that fall into the “toxic” category
- Rye grass staggers
- Lead
- Ivermectin/moxidectin
- Fluphenazine
List the differentials for central neurological disease of horses that fall into the “vascular” category
Post anaesthetic myelopathy
List the differentials for central neurological disease of horses that fall into the “inflammatory inflammatory” category
Polyneuritis equi
What is polyneuritis equi?
Abnormalities of cranial nerves and cauda equina
Describe the signs of rye grass staggers in horses
- Wide based stance
- Signs of cerebellar ataxia
- Muscle tremors
Explain how toxicity due to ivermectin/moxidectin can develop
Needs to be lipid bound to easy to overdose horses with lipid avialable e.g. foals, skinny horses
What is fluphenazine typically used for and what is the potential effect?
Used by trainers to calm horses, can cause seizure like activity
Define the grades of ataxia in horses
- Graded 0-5
0: Normal
1: Minimal deficits noted, required provocative testing to identify e.g. tight circling
2: Mild abnormality seen at walk
3: Easy to see ataxia at walk
4: Very ataxic, may fall with provocative testing
5: Recumbent, cannot stand
What is cervical vertebral malformation also known as?
Wobbler syndrome
What are the 2 types of cervical vertebral malformation in horses?
- Type 1: juvenile onset
- Type 2: mature onset
In which groups of horses if Cevical vertebral malformation commonly seen?
- Young, fast growing
- Weanlings, yearlings
- TBs and WBs
- Males
- Often seen earlier in racehorses as start training earlier, in others not until 4-5yo
- Horses given excess concentrate
Where is the compression from Cervical vertebral malformation in horses typically located?
C3-C5 typically
What does it mean when CVM is described as being functional or absolute?
- Functional: position of head can exacerbate the degree of ataxia
- Absolute: static lesions causing static spinal cord compression
List the clinical signs of Cervical vertebral malformation in horses
- Bilateral ataxia
- Dysmetria and spasticity
- Gradual onset
- Often associated with trauma
- May flare up
Describe the ataxia seen in CVM of horses
- HL worse than FLif lesion C3-C5
- FL similar/worse than HL if lesion C5-T1
- Flexor weakness leading to toe dragging
- Extensor weakness (walking tail pull)
What are the predisposing factors for CVM type 1?
- Young horses <2yo
- Nutritional: high plane of energy and high protein
- Genetic: more common in certain breeds
Describe the development of CVM type 2
- Old horses
- Osteoarthritis of cervical articular articulations (new bone covering intervertebral space, extends into spinal cord, initially soft tissue then bony compression of spinal cord)
- May be traumatic in origin
- Typically C5, 6, 7, may be asymmetrical
List the tests used in the diagnosis of CVM of horses
- Radiography
- Myelography
- CSF
- Electromyelography
Describe the radiographic findings that are suggestive of CVM
- Stenosis, osteoarthritis
- Minimal sagittal diameter and sagittal ratios
- Changes in caudal epiphysis of vertebrae (processes, ski-jump appearance)
- Sagittal ratio: divide width of spinal canal by width of corresponding vertebral body at cranial aspect of widest point, <50% ratio = 80% chance of compressive lesion on myelogram. >50% ratio = 20% chance horse has CVM
When is myelography indicated in the diagnosis of CVM in horses?
If contemplating surgery
Describe the method for myelography of suspected CVM in horses
- Standing or GA
- inject radiographic contrast media into intrathecal space
- Radiogrpahs in neutral, flexion and extension
- Minimum of 12 films
- May not always find lesions
What findings would be indicative of CVM on myelography?
- Compression of dye column
- 25% reduction of dye column at site that is affected
- May not always find lesion
Describe the CSF of a horse with CVM
Usually normal
What are the sampling sites for CSF in horses?
- Caudal sample from lumbosacral space
- Atlantoaxial joint
- Atlantooccipital joint
What may be found on EMG in a horse with CVM?
Occasionally cervical denervation
Describe the management of CVM in the horse
- Intra-articular glucocorticoids
- Exercise and nutritional restriction
- Surgical stabilisation
Outline and evaluate the use of surgical stabilisation in the treatment of CVM
- Decompression and cervical stabilisation
- Remove soft tissues, drill Bagby basket into affected joint space
- Bone graft and fuses joint
- Likely to generate only 1 grade of improvement
Outline the factors that should be considered prior to surgery for the treatment of CVM
- Duration of ataxia
- Age of horse
- Severity
- Co-existing conditions
- Intended use post surgery
- Owner commitment (horse likely to still have some ataxia after)
- Sites affected and whether this is dynamic or static
- Poor prognosis for trotters vs pacers
- Patience required, will take 1 year for results
- Management of owner expectations
How does surgery for CVM work?
- Allows fusion of vertebra over time
- Fusion resolves vertebral instability
- Bone remodelling takes place
- Prevents spinal cord compression
- Gradual improvement of neurological function
Describe the clinical presentation of Equine Degenerative Myeloencephalopathy
- Similar to CVM
- Symmetric tetraparesis and ataxia
- Worse in HL
- Hyporeflexia
- Young horses (birth to 2yo)
How is EDM diagnosed?
- Diagnosis of exclusion - CSF, blood, spinal radiography and EMG all normal
- Once everything ruled out, euthanase and confirm diagnosis at PM
Describe the pathophysiology of EDM
- Neuroaxonal dystrophy of cervical spinal cord and brain stem sensory and proprioceptive nuclei
- Fibre degeneration of ascending and descending pathways
- vit E/selenium deficiency allowing free radicals to cause damage
What are the main differences between CVM and EDM?
- CVM: abnormalities seen on radiography, myelography and sometimes EMG, no abnormalities in EDM
- EDM can be seen in wild equidae, CVM is not
What would these findings on necropsy be indicative of in a young horse with symmetric ataxia and hyporeflexia?
Neuroaxonal degeneration of brain stem, cervical and thoracic and lumbar spinal cord
Equine Degenerative Myeloencephalopathy
Outline the treatment of EDM
- Generally valueless
- High doses of vit E occasionally useful
- Not curative, once damage done, will not recover
How can EDM be prevented?
- Vitamin E supplementation daily for 2 years
Describe the clinical signs of EHV-1
- Abortion, stilbirth, weak foals
- Respiratory disease
- Neurological disease - myeloencephalopathy
- Ataxia, acute recumbency usually seen
- Oedema of scrotum, distal limb, pyrexia
- Symmetrical HL ataxia
- Urinary bladder paralysis (dribbling urine)
- Decreased tail tone
Describe the pathogenesis of neurological disease by EHV-1
- Causes vascular endothelial disease due to antigen-antibody complex formations
- Vasculitis and thrombosis with secondary CNS necrosis
- Cell associated viraemia
Describe how horses can contract EHV-1
- Inhaled pathogen from nasal secretion, fetal or placental tissue
- Direct spread between individuals most important
- Humans can act as fomites
- Can persist in trigeminal ganglia and be reactivated
What methods are used in the diagnosis of EHV-1?
- CSF
- Serology
- Virus isolation
- Response to treatment
What findings on CSF would indicate EHV-1?
Xanthochromia, low cellularity
What findings on serology would indicate EHV-1?
4 fold increase - 80% of UK herd exposed to EHV previously so serology may be positive even if not currently infected
Outline the method of viral isolation for diagnosis of EHV-1
- Nasal swab
- Heparinised whole blood
- Thick buffy coat and viraemia
- Need to be in chronic phase of infection in order to get results
Describe and justify the treatment of EHV-1
- Corticosteroids: dex 0.1mg/kg
- Acyclovir (poor bioavailability in the horse)/other cyclovirs/interferon
- Nursing care e.g. urinary bladder management, turning recumbent horses
- Dimethylsulphoxide (DMSO)
Why are corticosteroids important in the treatment of EHV-1?
Is an autoimmune caused condition
Discuss the use of DMSO in the treatment of EHV-1
- Anti-inflamm
- Free radical scavenger
- Some evidence, but poor, for effects in CNS in large animals
- Unlikely to do harm
Outline the control of EHV-1
- Isolation of affected animals
- Follow HBLB code of conduct
Discuss the prognosis of a hrose with EHV-1
- Good if mild (able to stand and walk), can return to normal function
- Guarded if recumbent, some do recover, others die (lots of comorbidities if recumbent e.g. anorexia, msucle damage, inability to urinate)
Which equine herpes viruses cause neurological signs?
EHV-1 and EHV-4
What causes Perennial Grass staggers in horses?
Mycotoxin Neotyphodium lolii
Explain how horses become affected by perennial rye grass staggers
- Mycotoxin taken up by plants and concentrated in leaves, esp. old leaves
- Heavily grazed pasture is risk factor
- Ingestion of leaves or imported rye-grass hay commonly causes disease
Describe the signs of perennial rye grass staggers in horses
- Spinovestibulocerebellar disease
- Ataxia, muscle tremor, dysmettria
- Worse with exercise
- Tremor incl. eye muscles
- Tends to occur in outbreaks
- Recover spontaneously
Where is perennial rye grass staggers more commonly seen?
Uncommon in UK, more in Southern Ireland (wetter)
Describe the prevalence of Equine Protozoal Myeloencaphalitis (EPM)
Exotic to UK, common in USA (50% of horses in USA seropositive) - may be seen in UK in horses shortly after import from USA
What causes Equine Protozoal Myeloencephalitis?
- Sarcocytis neurona
- Neospora Hughesi
- Single protozoan, migrates through CNS and spinal cord causing very focal disease, can sit in single spinal cord tract
Describe the clinical signs of EPM
- Often unilateral disease, very bizarre signs (pretty much anything)
- Asymmetrical ataxia, head tilt, hyperaesthesia
- Unilateral gluteal atrophy
- Paresis
- Horner’s syndrome
- Mastecatory atrophy
- Is multifocal, necrotic and non-suppurative
How is EPM diagnosed?
- Blood serology (only shows exposure)
- CSF antibodies (Western blot, variable, suggestive but not diagnostic)
- Definitive requires neurological deficits, antibodies in CSF, lesions in PM (lymphoid perivascular cuffing, macrophages and eosinophils)
What is the treatment for EPM?
Folic acid inhibitors
Describe the prevention of EPM
- Elimination of opossums (important vectors)
- Prevent access of opossums to feed
- Remove carrion
Name the Arboviruses that cause neurological disease in horses and state how they are spread
- Arthropod borne
- Flaviviridae (West Nile Virus)
- Togaviridae
Discuss the importance of the neuropathy causing Arboviruses
- Zoonotic, cause large scale losses
- Flaviviridae less severe than Togaviridae
- Both exotic to Uk and notifiable
- Flavi unlikely to be risk to Uk as mosquitoes required for spread not present in UK
Name the 3 types of Togavirus and state their prognosis
- Eastern Equine Encephalitis: very poor prognosis
- Western Equine encephalitis: Fair prognosis
- Venezuelan Equine encephalitis: very poor prognosis
Describe the disease caused by Togavirus
- All 3 types cause diffuse cerebral disease, are neutrotropic
- Clinical signs: fever, colic, anorexia
- Acute/peractue CNS signs: dementia, ataxia, seizure, blindness
How can Togavirus be controlled?
Vaccination
Give the reservoir and vector for Arboviruses
- Reservoir: birds
- Vector: mosquito
Describe the clinical signs of West Nile virus in horses
- Caudal spinal cord involvement
- Ataxia, hyperaesthesia, muscle fasciculations, weakness
- Milder clinical signs than Togavirus
What is the prognosis for West Nile Virus in horses?
60% recover, worse if <5yo, recumbent, weak. Some may relapse
Describe the diagnosis and treatment of West Nile Virus in horses
- Diagnosis: antigen/antibody in CSF/blood
- treatment: nursing, anti-inflammatory treatment
Discuss the use of vaccines in the control of West Nile Virus in horses
- Vaccine available
- But mortality and morbidity falls as becomes endemic
Describe the clinical signs of Japanese encephalitis (flavivirus)
- Mania
- Hyperaesthesia
Describe the clinical signs and control of Hendra virus in horses
- Death in horses (and humans)
- Some neuro signs
- Vaccine available for horses
Describe the clinical signs of rabies in horses
- Same as other species
- Aggression (rare)
- Hyperaesthesia
- Paresis/paralysis
- fever
- Ataxia
- Seizures
What causes hepatic encephalopathy in horses?
Toxic effects of ammonia and other false transmitters
Explain the mechanisms of hepatic encephalopathy in horses
- Liver failure = unable to break down intestinal NH3
- Congenital abnormality e.g. portosystemic shunt (rare)
- Primary gastrointestinal disease (e.g. severe colic, gastritis) leading to overproduction of NH3 by intestinal flora, exceeding rate of metabolism
Describe the clinical signs cerebral dysfunction as a result of hepatic encephalopathy
Seizures, circling, head turn, head pressing
Describe the management of hepatic encephalopathy in horses
- Reduce ammonia production by flora through use of antibiotics
- Drugs that reduce uptake of ammonia
What is Perinatal Asphyxia Syndrome in horses and what is it caused by?
- Aka Hypoxic Ischaemia Encephalopathy, Dummy Foals, Barkers, Neonatal maladjustment syndrome
- Multisystemic condition of newborn foal: neuro, GI, urinary
- caused by perinatal asphyxia due to unobserved foaling or red bag delivery
Describe the presentation of Perinatal Asphyxia Syndrome
- Appear normal for first 12-24 hours (i.e. stand and suck)
- Then become recumbent, lose suck reflex, start to seizure, resp centre depressed (apnea)
- Wandering, head pressing, vocalisation, dysphagia
- Seizures, head tilt, blindness
Describe the non-neurological signs of Perinatal Asphyxia Syndrome in horses
- Hypotension: reduced GI blood flow, necrotising enterocolitis, ileus, reflux, colic
- Oliguria
- Apnea
- Pulmonary artery hypertension: hypoxia and acidaemia (maintains fetal circulation)
- Glucose metabolism affected
- Secondary sepsis (due to recumbency)
Describe the management of Perinatal Asphyxia Syndrome
- 7-10 days intense 1to nursing, very expensive
- Anticonvulsant diazepam
- Respiratory (ventilator for several days), circulatory and renal support
- Must be hospitalised
What is narcolepsy?
Excessive daytime sleepiness, with REM sleep occurring +/- cataplexy
How does narcolepsy develop and how does i affect the daily life of the horse?
- Pattern of sleepiness
- Can be roused with stimulation
- Usually safe to work and will not sleep while ridden but may collapse if stop working for long periods
Which horse breeds are predisposed to narcolepsy?
Suffolk, Appaloosa, miniature horse, Shetland, Fell, Welsh pony
What are the main mechanisms of collapse?
- Brain not keeping animal upright/conscious
- Nerves not working
- Muscles not working
List diseases of the horse that may cause collapse due to the brain not keeping the animal upright/conscious
- Vestibular disease
- Cerebellar disease
- Metabolic disease
- Pressure
- Epilepsy
- Narcolepsy
List the diseases of eh horse that may cause collapse to the the nerves not working
- Motor neurone disease
- Myasthenia gravis
- Electrolyte abnormalities interfering with conduction
